This disclosure relates to a server system, such as a data center, with computers capable of operating at multiple performance points and in particular to a server system having a first operating point having a high energy efficiency performance and a second operating point having a high processing performance.
Server systems, such as those found in data centers for example, are configured with numerous computers systems that are arranged to provide computer-processing services to users. Typically, the computer systems are arranged in racks that electrically connect the individual computers to the users and other computers. A standard size rack may accommodate up to 40 to 80 computer systems per rack. The computer systems may include a number of components, including one or more processors, micro controllers, semiconductors, memory devices and the like. Each data center may have many racks of computer systems operating simultaneously.
During operation, the computer systems generate significant amounts of thermal energy. Typically, each computer system may generate on the order of 200W-250W of heat. In general, the semiconductors, such as CMOS based semiconductors have faster performance and lower power usage when operated at colder temperatures. Therefore, for reliability and performance reasons, the data centers include extensive cooling systems to dissipate the heat generated by the computer systems. The racks are usually located within a specially designed room that maintains proper environmental conditions by the cooling and conditioning of the room's air. The cooling of the computer systems is accomplished by moving the cool and conditioned air over the computer systems. The air is subsequently removed from the room and reconditioned for subsequent use. The cooling system for the data center may include a number of components. These components include one or more chillers, humidifiers, air conditioning compressors, condensers, fans and pumps.
Data centers are desirable since they have a much higher utilization rate, on the order of 25% when compared to distributed personal computers and servers that typically have a utilization rate of 1-3%. However, the typical data center has an electrical efficiency of only 30% due to the ancillary equipment needed for operations consume the remaining 70% of electrical power used by the data center. Since the computer systems used in the data centers continue to operate at faster speeds, the temperatures at which they operate is also at correspondingly higher. Therefore, the cooling system and power conditioning required for the operation of the data centers will continue to consume an increasingly larger portion of the electrical power used by the data center.
The cooling systems used in the data center are sized to perform under maximum, or worst case situations. Typically, the data center will operate at maximum operating conditions for less than 10% of the time. Therefore, for a large portion of the time, the cooling system is under utilized, but still consuming a large amount of electrical power. The size of the cooling system if further complicated by the thermal resistance between the computer-system components, such as the processor for example, and the air. To provide adequate performance, the cooling system needs to cool the air to provide a 60° C. temperature gradient between the computer processor and the cooling air. Therefore, if the data center desires to operate the computer processor between 75° C.-85° C., the cooling system needs to provide air at a maximum of 25° C. Due to inefficiencies in the distribution of air within the data center, the operating point for the conditioning system needs to be considerably less.
As a result of the complexities of existing data center cooling systems, the data centers have considerable electrical power requirements. A recent study estimates that the waste energy from a medium sized data center is equivalent to almost 3250 MWh of fossil fuel and 630 tons of carbon dioxide per year. In light of treaties entered into to help lower emissions of greenhouse gases, some countries have introduced a tax on carbon monoxide emissions. The tax may be as much as $85 per ton of emissions. These types of programs can have a dramatic impact on the financial viability of a data center.
While existing server systems are adequate for their intended purposes, it is desirable to have server systems that are capable of adapting their operation to provide high performance during peak periods while minimizing energy requirements during the off-peak periods.